IEEE 802.3 is a collection of standards and proposed standards relating to the physical layer (i.e., the PHY layer or simply PHY), and the Media Access Control sublayer (i.e., the MAC) of the data link layer, for wire-based Ethernet. For example, IEEE 802.3-2008 describes 1000BASE-T and 10GBASE-T. Prior to IEEE 802.3-2008, an earlier description of 1000BASE-T was made available in IEEE 802.3-2005 and IEEE 802.3ab-1999. Similarly, an earlier description of 10GBASE-T was made available in IEEE 802.3an-2006.
In general, a MAC device and a PHY device are associated with each port of a data communications device. The MAC device generally handles generating and parsing physical frames of data. Furthermore, the PHY device generally handles moving the data to and from the wire.
A processor typically queries the PHY device for link status to determine whether a link is up or down. In particular, if the PHY device returns a LINK_UP value, the processor considers the link to be up. However, if the PHY returns a LINK_DOWN value, the processor considers the link to be down and can take remedial steps to maintain reliable network operation such as utilizing a different network path to convey information between two end devices.